Signaling system.



I.. H. DAYRROW.

SIGNALING SYSTEM.

APPLICATION FILED OCT. 30.1917.

l ,283,687. Patented Nov. 5, 1918.

3 SHEETS-SHEET l.

IN V EN TOR. [/.Harmw AATTORNEY L. H. DARROW.

SIGNALING SYSTEM.

APPLICATION FILED ocT. 3o. |911.

Patented Nov. 5, 1918.

' 3 SHEETS-SHEET 2.

N s lfl N z s s "l r II- N IN VEN TOR. L Hamw ATTORNEY L. H. nARnoW.

slGNALlNG SYSTEM.

APPUCATION FILED OCT. 30. |911.

INVENOR.

up BY p A TTORNEY Patented Nov. 5, 1918..

LEO nipAimow, or NEW Yoi K.N.-.Y., AssreNon'moAMERIoAN.TELEPHONE ANi?4 A TELEGBAPHpooMPANY, A CORPORATION oF'NEw YORK.'l

SIG-NALING- SYSTEM.

To all whom z'zgmay concern;

Be it' known lthat I, yLEO DARROW,A residing at New York,-inthe county of New -York and yState of New York; have invented Y certain Improvementsin` Signaling Systems,

of '-which the following is a specification.v

This invention Trelatesg'to apparatus for*V use inf connection 'with telephone s'witchA boa-rdsbandiniore particularlyrelates to equipment tor-f privateV branch exchange" switchboards withwhich are associated both long vdistanceand ilocal' lines.

vItisone vof the objectsof the inventiontoA provide I a means; whereby g Va connection,`l

whichr will insure agood grade lof transmis,-

sionand propersupervision, be made" between two longadis'ta'nce lines terminating;

at a siiutchbijardyorfbetween a longdistance lineand'fone of the local circuits terminat-f ingat the switcl1board ,fsuch as an extension? orbetwe'en "a longdistance line'and a cen# tral oiiicie; A furtherfobject consists in the provision`- ot vap`parz u; i'i 's` which y will Yprevent* 7 a long .distance connection from being made with any cordcircuit ex'ceptthegproper 'long distance i'cor'd'i l'circuit; and Vthus ,obviates the i possibilityof E poor; transmission and improper 'supervisicn,- whichl wouldresult if lines as well asiocal' linesrit 'has been Afound advantageousin accordance with this invention" tof addto'the customaryV apparatus at such aswitchboard a" special type of cord* 'circuit` for -'making lo'ng distance connections. This is because it 'is'necessaryfto prow vitle'for a., better grade/'or'transmission in thccor'd-i'circu'its" us'e'dto makelong distance connections than'isrequired in the usual typeV of cord" circuit usedffor "local connec; tions. To 'nieetgthe 'demand' for' equipment which will serve such-a purpose thec'ord Vcircuit included -in this inventionhas beenj provided; together with special apparatus asso- 'ciated Awith the jacks of the lines't'erminating' :at the switchboard. To' obtain the best results '-it is yprovided `that vonly when'the long ldistance cord-circuitis used, can a long distance connectibnf'be completed. For this purpose there is connectedto the' sleeve'eon- Specication of Letters Patent.

Other i and` further ob;v

whilethose illustrated at the lower Patented Nov. 45, 191.8

Application iled October 30, Serial 'N 027199330'.-

tact of each of the acks ofthe long-distance linesa relay responsive toV current'zof lde-'jV nite polarityonly. These polarized relays control mechanisms `'to connect or disconnect I the long distancetran'srnission lines'and the apparatus terminating `at the contacts of 'the jacks; At the switchboard is located a di'- videdf battery which`=fis so connected tothe plugs ofthelong distance and local cord* circuits that there'are oppositepotentials on the l sleeve contacts thereof.

The potential on the sleeve contacts of the l. plugs of the long-distancecord circuitisiof lthe proper polarity to operate the aforementioned polarized relays associated with the long distance jacks,-'wh ich'upon functioning allow the long distance connection to be completed. On the other hand'the potential applied to the sleeve contactsof`the 'plugs' of the local cord circuit is of the opnositefpolarlty and will notJ operate the aforementioned polarized relays.V Accordingly a long distance connection can not be completed by using the local cord circuit. Moreover upon plugging 'in with the long distance7 cord thereisautomatically broughtinto the circuit apparatus adapted :torfunctioning with the particular type oflines connected.vr This is accomplished/by having'lsuch apparatus under the control'of two marginal relays with their `windings in series in, the sleeve conductor of the calling plug of the long distance cord. Then this plug is inserted in either `a long distance jack',` an extension jack; or the central oiiice jack, ya dii'erent combination of these rmarginal relays will be caused to functionand the desired apparatus under their control will vrthereby beassociated with the circuit.

The invention may now be more fully understood when taken inV connection with-thev accompanying drawing in which the Fig` ures 1, 2, and 3 when arranged side by side in numerical order illustrate diagrammatically the/preferred :torni of the invention. Inlthe Figs. l and 3 are shown the terminating .arrangements of 'the Various types of lines which' appear before the loperator in thel form of jacks located at the switchboard. Thejacks shown at the upper portions'of the drawing are the type of jack at which the long distance lines terminate,

lines or extensions. The jack shown in the middle port-ion of Fig. 3 is the type of jack suitable for use with a trunk connected to a central oflice. In the Fig. 2 are shown the two types of cord circuits to be used at the switchboard. The cord circuit C shown in the lower portion of the ligure is the type of local cord circuit which may be used to make connections between local circuits terminating at the switchboard or between a local circuit and the central office. The cord circuit A shown in the upper portion of the drawing is the long distance cord circuit embodied in the arrangement-s oic this invention. The long distance cord circuit A may be employed to make connections between two long distance lines terminating at the switchboard, or between a long distance line and one oit the local circuits terminating at the switchboard, or between a long distance line and the central. oliice.

Connected to Jthe sleeve contacts of the lOng distance jacks J, and J2 are the relays l and 2 which are constructed to respond only to current of a certain polarity. These polarized relays control the operation of the cut ott relays 3 and fl which serve to coin nect the transmission lines to the terminals of the jacks at the switchboard. The relays 5 and 7, and 6 and S, control the operation of the line signal lamps f) and l0 respectively. Associated with the extension jacks J3 and l, are shown the usual relays 11 and l2 under control of which are the line signal lamps 13 and 1,4; respectively. Included in the arrangements of the central otlice jack J, is the relay 15 having a double winding. Une winding of this relay responds to ringing current from the central otiice and the operation ot the relay controls the signal lamp 15. An auxiliary circuit lor locking up the relay l5 is shown which includes the battery B and the second winding of the relay.

Included in the long distance cord circuit A are the calling and answering plugs I), and P2 respectively. Connected to the sleeve ot the plug is a battery B so poled as to furnish current or" the proper polarity for ,operating the polarized relay 1. In the conductor terminating `in the sleeve Contact of the calling plug l?, are the windings of two marginal relays 1 7 and 18, thesewindings being connected in series, and the other terminal ot the conductor bcing connected to the battery B which is also so poled as to furnish current ,of the proper polarity to operate' the polarized relay 2. lVhen the calling plug I), is inserted in one of the long distance jacks, such as jack Jg. these two marginal relays are not actuated as the polarized relay 2 included in circuit is ot high resistance. Accordingly transmission will take place directly over the talking conductors of the cord circuit without introducing the repeating coil 20 which is associated therewith and which is controlled by one of said marginal relays. 'Iwo of the windings of this repeating coil are included in a bridge across the talking conductors of the cord and include a condenser and the relay 21. Vhen either distant operator rings over the line the relay 2i, will operate and cause the signal lamp 29 to glow.

llhen the calling plug P, is inserted in one of the extension jacks, such as jack J4, the resistance in the sleeve circuit is sut iiciently reduced so that the marginal. relay 17 will be caused to operate. This relay controls the operation of the relay 22 which, upon actuation, connects the repeating coil 20 to the talking strands of the plug P1. The relay 22 also closes a parallel path in* cluding the conductors 26 about the winding of the signalcontrolling relay 21. Upon the operation et relay 17 a circuit is also closed through the signal lamp 23 which then opcrates as a supervisory signal. Connected to the right hand windings of the repeating coil 2O is the divided battery B B which serves to furnish the talking current for the circuit closed through the repeating coil 20 by the releasing of the receiver hook at the extension station. The closing of this last niientioned circuit is indicated by the eX- tinguishing of the signal lamp 23 due to the cnergization of the relay 24 which is ineluded in the talking circuit.

When the calling plug P, is inserted in the central. oilice jack J5 both of the marginal relays 17 and 18 will be operated because the battery B included in the sleeve circuit of the jack J5 is now connected in series with the battery B in the sleeve circuit of the plug I)1 and the potential is thereby sufliciently increased. The functioning of rela 17 will, as formerly pointed out, cause the repeating coil 20 to be connected to the talking strands or the calling plug and will close a parallel path around the signal con trolling relay 21. The operation of the mar ginal relay 18, however, serves to disconnect the divided battery B B from the repeating coil as the talking current is now furnished by a source at a distant central oliice. Instead of being completed through the divided battery B B as formerly, the circuit is now completed through the retardation coil 27 and the relay 28, which. allows supervision on the central otlice trunk and provides for re-ring signals as will be hereinafter pointed out in the description of the operation.

Included in the usual type of cord circuit illustrated in the lower portion of Fig. 2 are the answering and calling plugs B, and PA, respectively. Connected to the sleeve contact ot the answering plug 1) is the thelong@distance-'jacks'. As there is no -bat-y tery connectedy ltothe- 'conductor terminating inthe sleeve of Lthecallingplulg P4 and as the battery lconnectedto=the-sleeve ofthe answerinzgV plug P3 isI no'tvof fa suitable polal'ity,the^polarifzed relays land 2 cannot be actuated by theinsertion of thefplu'gsP and Pg in the'flong distancejacks Jil' and Jn and 'accordingly a vilongdistance connectionv cannot'beE completed throughv the llocal cord circuiti." 'Located in la bridgef'across the talking lconductors ot the. local cord circuit'- is theimp'edance coil l inluding the: windings 30, 31, andh. v When'fa i connection is` com'- pleted between l'two extension stations,V this -bridge normally includes f the "windings 31 and-32:and thefb'atteryf Bgfthe latter supplying 'the tallkinglicurrentthroughfthe inn-pafA dance of-ltheltvvoflwindingsei However, when; a 'connection-is" made between ianextension rent eis "supplied from aY source at= -the centralL office vinstead Yof from the' battery B- jlcate'd atthe lprivate branchexchangehboard. Accordil'igly-bymeans of -)therelay Slconnect- B is disconnected l"fr-cnrthe!Wind-ings ofi/ the impedance'coilz -1- -andfthel'ocking Winding of;1 a supervisory relay ASES-is substituted-theres for: By' means Ofthfei relays` Sti-rand 53'? the sufticiently increasing ithefrnpedance tofpre-y ventf talking; curlrent rfrom being-'shunted 1 therethlrouglr.4 "-'Connecte'd' to the lsleeve offV the plug P3 isthesignalflamp 34 kso arranged-- therethrough*Lupenv the@ insertion of'the plug-` P-s' in thefj ack Jg were -it notl 1 for l`"the fact 1 that this"fci-rcuitfis-heldifopen by the energiir zation of th'e rela-yB'lassociated W-itlr one of` dfrelay becomes. deenergize'dand'itsTarmaturehV retractsL andi-*allows the circuitI through-the signal f lam-pf 34E-"1` to #bee complet-ed:j By `the*- ab'o'vedescribed meansX the operator 1 -at the switchboardf may be informed 'Whenl con- -ver'sation between twoA extension stations has@ been fterniinated." 1 V'hen a connection is made #between an rex-tension station and the cent'raljs office' thev operation'A ofthe signal?` lamp maybecontrolledfether by the rei' -lay'- 33 or by-'thelrelay which bridged?V across the-1 line lover thefcontacts of relays iand 37k By such-arrangements f the op eratorfat thedprivatebranchenehange board Y' may be informed'whens the connection is tera 'recallis desired by 'thef-centralf0ice vrAs' the* llocal lcord-Icirtmit thus briefly describedis of the usual type andL-doesinotconstitutea part of this invention,v no urtherf descriptionfthereovwill be'necessary andthe dea scription 'of 2 its operation will lbe omitted.

The inventi on 'mayA noivbemore 'fully A un-f dei-stood from" the' Jfollowing descriptions of l its operation.- If`a call isloriginated-from the distant 'endfoverone o-thief-long dis-5 tance lines such asgfor eXa111p-le;the line Li, ringing` current Will be' transmitted over7 the line L1 and-thewinding of relay-7,`=which will beenergized Landlpull -upjits armature f thereby closingthe `following circuitldromfv ground; armature zfand cor'it'act-v of A"relay 75 over conductr i37,` filament of "signal-f -lafmp- 9 to battery B andfgroundf llTlr-is causes-"thesignal lam-'p '9v tol glow# andthe opera-tor at the yprivate branch' exchange is` tl'ierebyfnotiffied that 'a connectionlis desired vflhe'fpull-i ing up'of its armature by1-relay 7' also closesa circuitthrough the"'Windingl of relay5 `to battery B and ground; causing relay `5 to become energized 'and pull" upits ari-nature and closeV a locking circuitifor 'the signalflamp 9 over tlieconductor leading to-theflefthand contact land armature offlth'epolarized -v-relay the polarized rela-y'l to becomelenergizedlf and thereby'fclosesa circuitfrom ground,-

armature Eand right hand Contactl of'i relay 1, conductor 38', Winding of relay 3, to battery B and ground. This energizes relay 'Bfwhich pulls up itsari'natures, therebydisconnectingthel'long distancetransmissionI line L1 from' the` conductors leading to thevwinding rel 7k and connecting the transmission'- lline to 'the Vconductors terminating in; thenl tip and Vringcontacts ofv thefjackJ 1.- The energization oflthe Vpolarized relay' 1- also ser-vesto extinguish the linelsign'al lamp 9` asthe'lockingeircuit `fori'nerlyclosed therethrough over the left handfconta'ct and armature cofrelay 1 is broken by vtheenergization of'saidrelay.

The operator by non'r throwing'fher listening key Ki'rmay establish a connection*betweenl tlie operators set and 'the call-,ingA station over thecontac-ts of `key Ki, talkingg'st-rands of =cord"circi'1it1 A, contacts f of I plug-Q :P2 and jack J 13 conductors' 39 =andf405 contactsland"v armatures of' relay *13, and loverfthelongfdistance transmissienfline' 'Ato-the calllngg sta-` whether a connection with another long distance line, with an extension station, or with a central oiiice is desired.

li? the connection desired is with another long distance line, as for example the line L, terminating at the switchboard in the jack J2, the operator inserts the calling plug P, of the long distance cord circuit in the jack J2. This closes the following circuit; from ground. and battery B', Winding of relay 18, conductor 41, winding ot relay 17, conductor leading to sleeve oi plug P1 contacts of plug P1 and jack J2, winding of polarized relay 2 to ground. As the current furnished by the battery B is of the proper polarity, the closing of the above described circuit will. cause the polarized relay 2 to become energized and pull up its armature thereby closing the following circuit; from ground, armature and left hand contact of relay 2. conductor 42, winding ot relay 4, to battery B and ground. The closing of this circuit energizes relay 4 which pulls up its armatures and connects the long distance transmission line L, t') the conductorsl 43 and 44 leading to the tip and ring contacts of jack J2. The operator then throws the ringing key K2 and sends ringing current over the long` distance transmission lino L The called station now responds to this ringing current and a connection is completed between the two long distance stations over the following circuit; vtrom the calling station, over the long distance transmission line L1, to armatures and contacts of relay 3, over conductors 39 and 40, tip and ring contacts of jack J, and plug P2, closed contacts of ringing key Km over the talking strands 45 and 46 of the cord circuit, contacts and armatures of relay 22, closed contacts of ringing key K2, tip and ring contacts of plug P, and jack J2, conductors 43 and 44, contacts and armatures oi relay 4, and thence over the long distance transmission line L2 to the called station, l/Vhen the long distance call is terminated by either subscriber hanging up his receiver the operator at the distant central oliice associated locally with the subscribers set is notiiied thereof by the usual type of line signal and thereupon sends ringing current back over the talking circuit to the private branch exchange herein illustrated. T his ringing current passes over the talking strands 45 and 46 of the long distance cord circuit and over the bridge across said talking strands. This bridge includes the left hand windings of the repeating coil 20, the conductors 47 and 48, a condenser, and the winding of relay 21. The relay 21 is adapted to respond to ringing current and is accordingly energized and by pulling up its armature closes the following circuit; from ground, armature and contact of relay 21, over conductor 49, filament of signal lamp n29, to battery B and ground. The closing of the above described circuit causes the signal lamp 29 to glow and the operator at the private branch board is thereby in formed that the long distance call has been terminated. Associated with the signal lamp 29 is the relay 50 which becomes energized by the actuation of the ringing responsive relay 21 and by pulling up its armature becomes permanently energized by closing the following circuit; Jfrom ground and battery B, winding of relay 50, contact and armature of relay 50, and thence over the conductor leading to Contact of key K1 and ground. This energization of relay 50 also closes an auxiliary circuit through the signal lamp 29 and causes it to glow after the ringing current has ceased and until the private branch exchange operator breaks the circuit therethrough by throwing the key K1.

If the operator at the private branch exchange ascertains that a connection is desired by the calling subscriber on the long distance line with one of the extension lines, as for example the line L4K terminating at the switchboard in the jack J4, she inserts the calling plug P, of the long distance cord circuit in the extension jack J, and by throwing the ringing key K2 transmits ringing current over the line L, to the extension station. When the plug l?, is inserted in the jack Jl, the Jfollowing circuit is closed; from ground and battery B', winding of marginal relay 18, conductor 41, winding of marginal relay 17, sleeve contacts of plug P, and jack J4, to ground. When the plug P, was inserted in the jack J2 the ycircuit closed through the windings of the marginal relays 17 and 18 included the high resistance of the polarized relay 2 and the marginal relays 17 and 18 were not energized. However, in the above described circuit closed through the marginal relays 17 and 18 by the insertion of the plug P, in the jack J the resistance is suiiiciently reduced, as the sleeve contact of jack J4 is directly grounded, so that the marginal relay 17 is caused to respond. The actuation of the marginal relay 17 closes the following circuit; from ground, armature and contact of relay 17, conductor 52, contact and armature of relay 24, conductor 53, contact and armature of relay 18, filament of signal lamp 23, to battery B and ground. By the closing of the above described circuit the signal lamp 23 will be caused to glow. The actuation of relay 17 also closes the following circuit; from ground, armature and contact of relay 17, to connecting point 51, thence through the winding of relay 22 to battery B and ground. The closing of this last mentioned circuit energizes relay 22 which by pulling up its armatures disconnects the talking strands 45 and 46 of the cord circuit from the conductors leading to the tip and ring YV V lanlp'v 29 to bejoperatedbyringing current'ff nected to the right '.handv windings of the re-.

vpeating. coil 20 by conductors 56 and 57,'1; :armatures and contactsfof relay 18, and conductors 55.1and. 54 is the 4.divided battery current. for 'theextension line Athrough the right hand winding of the repeating .coil 20. "Whentheballed subscriber atthe extension. stationremoves the receiver from. the vhook in-fresponse yto .the ringing signal, a talking l5 .1; circuit will-beclosed through .the right hand Y windings ozff the r`repeating coil 2O :is-follows;V

froml groundiand battery B, conductor 54 Icontactand armature of relay 185.v conductor v L coil.` 20,1.conductor 59 Contact andy .armature iofgrelay. 22, conductorfleadng to tip of plug Pi, thence through'-the.extension stationand v backI to .ring contact of plug. P1' byk way of 25 'lineY L4 and contacts.ojaclrJb-.overeenuductenleading.fromY ringy contact of xplug.v

P1, armature and contact of relay 22,10011-V seductor 58,@lower.:right-handlwindingof ref1 peatingcoil 20, conductonyarmature. and

gncontacntl ofA frelay 18,. conductorr fwinding A .OsrelayQ/Je, .to'batteryBand ground. The# bridge-across theftallring strands of the cord fi, .1, circuit.v whichA .includesathe leftY hand 4wind A. .21,the'zpullingnp of itsv upper armature by T tot relay 22.fcloses A ai. parallel pathY around the f-:2winding ofsaidzringing responsive relay by u means of the conductors 26 and the Ycon-y ;.f.denseri-100, .sol :thatfthisbridge is. now com- .`.-pleted-through the .upper leftihand winding! offrepeatingcoil 20,1 overconductors 26l `and A.condenser-100, 'and ithencethroughthe lower Y ix 11.1 left hand winding ofirepeatingcoil 20. Thel f this parallel. :pathzand togcausel .them .to be vtransmited througlrthe. windingofV theringi 'f `ing. iresponsivere ed out. Accordingly .theabove described ar- .rangements-provide a :low impedance path. through said bridge-.i fortelephonic currents, while at thesesametime allowing the signal fromthe longdistance line. In order that the operator maybe informed when- Athe -con-H fr nectionhas been terminated at .then extension L 135l station: the -.followingr'-.sjignaling i means are rB B', which serves to. furnish. the talking pletedin afldiierent manner by theY aforel; '.mentionedtenergization of relay'22. :While .'normallylthis bridge wascompleted through i'. nthe winding Lof/:the ringing responsive relay ay .21 iasgpreviously point-V provided vfor this purposes? `Whenith3talk` i ing circuiti through. the right hand: windings fof theirepeating coil- 20 isiicl'osedfathe-Lv relay .ginalurelzfxy 17. xAs soon as'thesubscriber attlie extension station terminates the con- `nectioni: andpbreaks` the ntalkingmcircuit .through the Arightlia'n'd windings :ofithe repeating .coil 2Q by hanging .rupi-hismeceiver, the relay 24 becomes 'de'e'nergizedland by allowing. its armature to retractcauses the above mentioned .circuity through the signal lamp 23V to be completed; whereupon -the vglowing of `the signal-lamp123 :willzinform .sqthe operatory `oi theziterinination of ther con- .57,. upperfrighthand-winding offrepeatinge- E f nection;`

If hel -OPelfOI- at. ther private Abranch eX- change ascertains: that a .connection lis; de-

sired by'. the .calling Vsi'ibscriber AonftheL- long Y distance line with a. central oiiice; suchl as is herein illustrated Vas being. associatedw-ithi theprivatebranch switchboard .bytheft'runk line L5 and Vthejaclr J5, sheinsertsgthecallingplug P11of-:the.long:distance cord4 circuit -niarginalrelay 17, sleeve contacts Aof'p-lug P1 and jack J5,- conductor 60 rto .batteryB and ground. As "the above described i circuit lclosed through the windings of theinarginal relays. -18 and 17 includes in: series the -battery Bi and ethe ybattery-lnrthe potential is i suliicient to cause. both 1.01:' -the'se' marginal a relays to become energized. As :has I .been Y .1in the jack` J5. lWhen..therplug'P1j isinseited v formerly. pointedV out greater detail, the

energization Vof the; marginal;l relay lZ serves lto disconnect-the talkingstrandsof the. long distance cord-.circuitV from. the conductors 1 terminating Yin .the tip.v andaring.. contacts of plug Pif-.fand conn'ectsfthe glatter" to` the'.con-

`ductors' 58 andY v5 9.-.le'ading to 'the rightfhand winding of the repeating coil 20,;th'e'reby inf clndingf the.. lright handk windings of s the repeating.- coil in the.centralyoilicetalking cire cuit; Also .inf the( saineV manner ras. .formerly :pointed i out, .the energizationf of. marginal relay'l .causesaparallel path .to beclosed -itsfarmatures. thereby; `.disconnecting the divided battery B= B. troni' .fthe right..hand windings of the repeatingycoil,v .as the. talking current fon this connection will bei furnished g from a, source atra. distant ...Centrali office. Accordingly the-.talking circuitisnowom- .eplete'd overl the central;` oiiice. .trunk andi the right hand windings of the repeating coil 20 as follows: from upper right hand winding of repeating coil 20, over conductor 57, armature and contact of relay 18, conductor 61, retardation coil 27, conductor 62, contact and armature of relay 18, conductor 56, to the lower right hand winding of repeating coil 20. The insertion of plug P1 in the jack J, and the completing of the above described circuit operates the customary line relay and signal located at the central oiiice and informs the central oiiice operator that a connection is desired. The pulling up of its lower armature by relay 18 connects the signal lamp 23 to the conductor 63 and places the signal lamp 23 under the control of relay 28. When the operator throws her listening key K1 a circuit is closed through the left hand winding of relay 28 as follows; from ground and Contact of key K1, conductor 64, left hand winding of relay 28, battery B to ground. This causes the relay 28 to become energized and by pulling up its armature its right hand winding becomes included in the central oiiice talking circuit by means of the conductors 65 and 66. Accordingly if the operator releases her listening key K1 and thereby breaks the circuit through the left hand winding of relay 28, the relay will still remain energized as long as its right hand winding is included in the central oflice talking circuit. When a re-ring signal is desired the central oliice operator throws her ringing key and sends ringing current over the talking circuit and through the winding of relay 28, instead of the direct current used for talking purposes. As the relay 28 will not respond to the alternating current used for ringing purposes it will become deenergized and allow its right hand armature to retract thereby closing the following circuit; from ground, right hand armature of relay 28, conductor 63, Contact and lower armature of relay 18, ilament of signal lamp 23, battery B, to ground. Accordingly the private branch exchange operator is notified of the re-ring signal by the glowing of signal lamp 23.

While the invention has been disclosed as embodied in certain specific arrangements it will be understood that it may be embodied in many widely varied organizations without departing from the spirit of the invention, as defined in the appended claims.

What is claimed is:

l. In a telephone system, a switching station, a plurality of local lines, trunks leading to main offices, and a plurality of long distance lines terminating at said switching station, switching means at said station whereby local lines may be interconnected and whereby a local line may be connected to a trunk, a second switching means adapted to interconnect two long distance lines, a long distance line and a trunk, and a long distance line and a local line, and means associated with the long distance lines and said second switching means to prevent the eii'ective use of said first mentioned switching means to establish a connection with any ot said long distance lines.

2. In a telephone system, a switching station, a plurality of local lines, long distance lines, and trunks leading to central oihces, having terminal arrangements at said switclr ing station, two cord circuits to connect various combinations ot' said Jterminal arrangements, a divided battery located at said switching station and so connected to said cord circuits that there are opposite potentials on the sleeve conductors of the plugs thereof, polarized relays with their windings in the sleeve conductors of each terminal arrangement of said long distance lines, said polarized relays being actuated only when the plugs of a certain one of said cord circuits are associated with said long distance terminal arrangements, and said polarized relays controlling means whereby said long distance lines may be connected to or disconnected from their respective terminal arrangements.

8. In a telephone system., a switching station, a plurality of local lines, trunks leading to main oiiices, and a plurality of long distance lines terminating at said station, a cord circuit adapted for establishing connections involving said long distance lines, two marginal relays in the sleeve conductor or' a plug of said cord circuit, neither of said relays being actuated when said plug is associated with one of said long distance lines, one of said relays being actuated when said plug is associated with one of said local lines, and both of said relays being actuated yvhen said plug is associated with a trunk ine.

4. In a telephone system, a switching station, a pluralit of local lines, trunks leading to main o ces, and a plurality of long distance lines terminating at said station, a cord circuit adapted for establishing connections involving said long distance lines, two marginal relays in the sleeve conductor of a plug of said cord circuit, neither of said relays being actuated when a connection is made with a long distance line, one of said relays being actuated when a connection is made with a local line, signaling means under the control of said relay for indicating the termination of said connection, both of said relays being actuated when a connection is made with a trunk line, and signaling means under the control of said relays for indicating a re-ring from said trunk.

5. In a telephone system, a switching station, a plurality of local lines, trunks leading to main oiiices, and a plurality of long distance lines terminating at said station, a cord circuit adapted for establishing connections involving said long distance lines, marginal relays with their windings included in a sleeve conductor of said cord circuit, means under the control of said marginal relays whereby, when a connection is made with a long distance line, transmission may take place directly over the talking strands of said cord circuit, and whereby, when a connection is made with a main ofiice, transmission will take place through a repeating coil associated with said cord circuit, and whereby, when a connection is made with a local line, transmission over the cord circuit will take place through a repeating coil with which is associated a source of high potential battery supply.

6. In a telephone system, a switching station, a plurality of local lines, trunks leading to main oilices, and a plurality of long distance lines terminating at said station, a cord circuit adapted for establishing connections involving said long distance lines, two marginal relays in the sleeve conductor of a plug of said cord circuit, neither of said relays being actuated when said plug is associated with one of said long distance lines, and means under the control of said relays when unactuated whereby transmission will take place over the talking strands of said cord circuit, one of said relays being actuaforementioned repeating coil is associated with said cord circuit and whereby said source of high potential battery supply is disconnected from said repeating coil.

In testimony whereof, I have signed my name to this specification this 24th day of Y October, 1917.

LEO H. DARROW.

i Copies of this; patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, iD. C. 

